The present invention relates to a device and method of making a porous membrane. More specifically, this invention relates to a microporous membrane that can be formed on the outer surface of the inflatable member of a balloon catheter.
A variety of surgical procedures and medical devices are currently used to relieve intraluminal constrictions caused by disease or tissue trauma. An example of one such procedure is percutaneous transluminal coronary angioplasty (PTCA). PTCA is a catheter-based technique whereby a balloon catheter is inserted into a blocked or narrowed coronary lumen of the patient. Once the balloon is positioned at the blocked lumen or target site, the balloon is inflated causing dilation of the lumen. The balloon is deflated and the catheter is then removed from the target site and the patient""s lumen thereby allowing blood to freely flow through the unrestricted lumen.
Although PTCA and related procedures aid in alleviating intraluminal constrictions, such constrictions or blockages reoccur in many cases. The cause of these recurring obstructions, termed restenosis, is due to the body responding to the surgical procedure. Restenosis of the artery commonly develops over several months after the procedure, which may require another angioplasty procedure or a surgical by-pass operation. Proliferation and migration of smooth muscle cells (SMC) from the media layer of the lumen to the intima cause an excessive production of extra cellular matrices (ECM), which is believed to be one of the leading contributors to the development of restenosis. The extensive thickening of tissues narrows the lumen of the blood vessel, constricting or blocking the blood flow through the vessel.
Stents, synthetic vascular grafts or drug therapies, either alone or in combination with the PTCA procedure, are often used to reduce, or in some cases eliminate, the incidence of restenosis. The term xe2x80x9cdrug(s),xe2x80x9d as used herein, refers to all therapeutic agents, diagnostic agents/reagents and other similar chemical/biological agents, including combinations thereof, used to treat and/or diagnose restenosis, thrombosis and related conditions. Examples of various drugs or agents commonly used include heparin, hirudin, antithrombogenic agents, steroids, ibuprofen, antimicrobials, antibiotics, tissue plasma activators, monoclonal antibodies, and antifibrosis agents.
Since the drugs are applied systemically to the patient, they are absorbed not only by the tissues at the target site, but by all areas of the body. As such, one drawback associated with the systemic application of drugs is that areas of the body not needing treatment are also affected. To provide more site-specific treatment, balloon catheters are frequently used as a means of delivering the drugs exclusively to the target site. The balloon assembly of the balloon catheter is positioned at the target site and inflated to compress the arteriosclerosis and dilate the walls of the artery. The therapeutic agent is then administered directly to the target site through small holes or apertures in the wall of the balloon assembly. The apertures through the balloon may be formed by mechanical punching, mechanical drilling, directing a laser beam at the elastic material, directing an ion beam at the elastic material, or directing an electron beam at the elastic material, among other possibilities.
Apertures formed in the walls of the balloon assembly offer many advantages to potential users. However, such devices may be deficient in their drug delivery characteristics. For example, when the balloon is filled with therapeutic or diagnostic liquids/fluids under relatively high pressure, fluid is ejected from the apertures in the form of a jet-like flow. The fluid jetting from the apertures is at such a velocity so as to cause tissue damage to the lumen or vessel wall. Since the rate at which the drug is released or delivered to the target site is a function of the structural properties of the apertures, drug release rates are inadequately controlled. As such, the balloon configuration greatly limits the usefulness of the catheter.
In view of the above, it is apparent that there is a need to provide a drug delivery device that delivers drugs, therapeutic agents, diagnostic fluids and the like deep within the tissue without causing damage to the tissue and significant systemic loss of delivered fluid materials. It is also desirable that the drug-delivery device allows one or more drugs to be released at controlled rates. There is also a need to provide a method of manufacturing such an improved drug delivery device that is convenient, efficient and cost effective.
In one embodiment of the present invention, the drug delivery device includes an elongated shaft, having a distal end and a proximal end, and an inflation assembly coupled to the distal end of the elongated shaft. The inflation assembly includes an inflatable balloon having a plurality of holes formed in the wall of the balloon. Further, a microporous coating covers a portion of the outer surface of the wall of the balloon. The thickness of the coating and the size of the micropores permit controlled delivery of a substance from the elongated shaft to the holes in the balloon and through the micropores of the coating covering the balloon.
Another aspect of the present invention is a method for making a drug delivery device. In one aspect of the invention, the method includes providing a catheter-based device having a porous inflatable member secured at a distal end of said device. A first solution and a second solution are applied onto the porous inflatable member to coat the outer surface of the porous inflatable member. The coating is then dried to produce a microporous precipitate on the outer surface of the porous inflatable member.
In general, drug(s) flow through the elongated shaft and into the inflatable member causing the inflatable member to inflate. Upon reaching a predetermined pressure, the drug(s) stream out of the holes of the inflatable member and disseminate from the pores of the microporous coating at a controlled release rate. Generally, the flow rate of fluid from the coated inflatable member is a function of the thickness and pore size of the microporous coating. As such, the microporous coating disperses the jet-like streams of liquid ejected from the holes of the inflatable member so that the fluid oozes or controllably exudes from the microporous coating to prevent the jetting effect from damaging tissue.